The present invention relates to a diaphragm-type carburetor for an internal combustion engine that operates with layered scavenging, especially for the two-cycle engine in a manually guided implement, such as a power chainsaw, a cut-off machine, a brush cutter, or the like. Formed in the carburetor housing is an intake channel portion in which is disposed the butterfly valve that is pivotably held by a shaft and in the vicinity of which fuel-conveying channels open into the intake channel portion. Such fuel-conveying channels are supplied from a fuel-filled control chamber that is formed on a longitudinal side of the intake channel portion of the carburetor housing and is separated from a compensation chamber by a control diaphragm. An air channel that additionally supplies air for combustion is formed in a component secured to the carburetor housing and has a throttle member that is rotatably held by a shaft and that is adjustable by being coupled with the position of the butterfly valve.
A carburetor of this general type is known from the Japanese publication JP 09268917 A. Disposed between the air filter and the carburetor housing is an intermediate piece that extends the intake channel portion and from which branches a connecting line that opens into the transfer port between crank case and combustion chamber of the connected two-cycle engine. During operation of the internal combustion engine, fuel-air mixture is drawn into the crank case via the carburetor, while via the connecting line into the transfer ports adjacent to their inlet openings fuel-free air for combustion is drawn into the combustion chamber. Therefore, when the transfer ports are opened, first combustion air by itself that was previously collected in the transfer ports flows into the combustion chamber and displaces the exhaust gases found therein to the exhaust valve. The fuel-free air for combustion follows the fuel/air mixture that flows out of the crank case into the combustion chamber. Such a layered scavenging lowers the scavenging losses that are unavoidable with two-cycle engines. Unfortunately, arranging an intermediate flange between the air filter and the carburetor for branching off the air for combustion by itself leads to a lengthening of the overall length, which creates problems where the space conditions are limited. Especially for portable, manually guided implements, the installation space provided for accommodating the carburetor and the air filter is very limited, for which reason the conversion of the layered scavenging is particularly problematic for such applications.
It is an object of the present invention to provide a diaphragm-type carburetor for an internal combustion engine that operates with layered scavenging, which such a carburetor having a short overall length while maintaining a small overall size.